This application is related to Japanese Patent Applications No. 2000-126161 filed on Apr. 26, 2000, No. 2000-279956 filed on Sep. 14, 2000, No. 2001-1535 filed on Jan. 9, 2001, No. 2001-43971 filed on Feb. 20, 2001, and No. 2001-50923 filed on Feb. 26, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a refrigerant cycle system suitable for an air conditioner for a vehicle and the like.
2. Description of Related Art
A conventional basic structure of a refrigerant cycle system is roughly divided into a receiver cycle and an accumulator cycle based on a difference between control of a super-heating degree of refrigerant at an outlet of an evaporator and control of a super-cooling degree of refrigerant at an outlet of a condenser.
As shown in the Mollier diagram of FIG. 52, the receiver cycle cools and condenses refrigerant discharged from a compressor 101 by a condenser 102, the refrigerant from the outlet of the condenser 102 is separated into gas and liquid refrigerant by a receiver 107 provided on the outlet side of the condenser 102. The liquid refrigerant from the receiver 107 is made to be expand and decompressed by a thermal type expansion valve 131, and then the low-pressure refrigerant after this decompression is evaporated by absorbing heat from air in an evaporator 104.
In this receiver cycle, since a gas-liquid interface of the refrigerant is formed within the receiver 107 and the refrigerant within the receiver 107 is maintained above a saturated liquid line L2, the super-cooling degree SC of the refrigerant at outlet of the condenser 102 is controlled to 0xc2x0 C. On the other hand, the thermal type expansion valve 131 feeds back the super-heating degree SH of the refrigerant at outlet of the evaporator 104 to automatically adjust a valve opening for thereby maintaining the super-heating degree SH of the refrigerant at the outlet of the evaporator 104 within a predetermined range (for example, 3 to 15xc2x0 C.).
On the other hand, in the accumulator cycle, as shown in the Mollier diagram of FIG. 53, a fixed restrictor 103 (fixed throttle) such as a capillary tube is directly connected to the output of the condenser 102 to directly decompress the refrigerant from the outlet of the condenser 102 in the fixed restrictor 103. Then, the low-pressure refrigerant after the decompression absorbs heat in the evaporator 104 for evaporation, and the refrigerant, which passed through this evaporator 104, is made to be flowed into an accumulator 108. Thereafter, the refrigerant from the outlet of the evaporator is separated into gas refrigerant and liquid refrigerant in the accumulator 108, and gas refrigerant within the accumulator 108 is sucked into a compressor 101.
In the accumulator cycle, since a gas-liquid interface of the refrigerant is formed within the accumulator 108 and the refrigerant within the accumulator 108 is maintained above a saturated gas line L1, the super-heating degree SH of the refrigerant sucked into the compressor 1 is maintained at 0xc2x0 C. Because the fixed restrictor 103 is used as decompression means, the super-cooling degree SC of the refrigerant at outlet of the condenser 102 is determined depending on flow amount characteristics of the fixed restrictor 103, a cycle high pressure and a cycle refrigerant flow rate, and the super-cooling degree SC normally fluctuates in a range of 0 to about 20xc2x0 C. because of fluctuations in cycle operating conditions.
However, in the former receiver cycle, since the thermal type expansion valve 131 feeds back the super-heating degree SH of the refrigerant at the outlet of the evaporator 104 to automatically adjust a valve opening, the receiver cycle system needs a complicate and precise valve mechanism, leading to an increase in cost.
In order for the thermal type expansion valve 131 to sense the super-heating degree SH of the refrigerant at outlet of the evaporator 104, there arises the need for setting an installation place for the thermal type expansion valve 131 in the vicinity of the evaporator 104, in other words, in a compartment. As a result, passage noise of the refrigerant, which occurs in a restriction passage of the thermal type expansion valve 131, becomes prone to propagate to an air conditioner user (occupant) within the compartment, and a problem of refrigerant passage noise becomes obvious.
In contrast, in the accumulator cycle, since the fixed restrictor 103 is used as the decompression means, this can be manufactured at exceedingly low cost as compared with the thermal type expansion valve 131. Since it is not necessary to place the fixed restrictor 103 in the vicinity of the evaporator, but the fixed restrictor 103 can be placed on the outside of the compartment (e.g., engine room side of the vehicle), there is an advantage that the refrigerant passage noise to be transmitted into the compartment can be greatly reduced. However, in a refrigerant cycle system for vehicle air conditioning, however, because the compressor 101 is driven by a vehicle engine, the number of revolutions of the compressor 101 also fluctuates greatly with the fluctuation in the speed of the engine. For this reason, if the fixed restrictor 103 is used for the decompression means, a refrigerant flow adjusting operation cannot be correspond sufficiently to the great fluctuation in the number of revolutions of the compressor 101 to greatly fluctuate the super-cooling degree SC of the refrigerant at outlet of the condenser, resulting in excessive fluctuation width. For example, when the compressor 101 is revolving at high speed, the compressor discharging capacity is increased, and the high pressure discharged from the compressor 101 is increased so that the super-cooling degree SC of the refrigerant at outlet of the condenser becomes too great. This occurrence of the excessive super-cooling degree SC causes an increase in a compressor driving power due to the increased high pressure to worsen the cycle efficiency.
In addition, there is another disadvantage that the accumulator 108 has inferior mountability. More specifically, the accumulator 108 is provided at the outlet side of the evaporator 104, that is, in a low-pressure passage, for separating gas-liquid of the low-pressure refrigerant having a large specific volume, it is necessary to make the capacity of the accumulator 8 larger than that of the receiver 107 provided at the high pressure side. Accordingly, when the refrigerant cycle equipments are mounted within such narrow space as the inside of a vehicle engine compartment, the mountability of the accumulator 108 will be more worsen than the receiver 107.
In view of the foregoing problems, it is an object of the present invention to provide a refrigerant cycle system with an improvement structure, which readily controls a super-heating degree of refrigerant discharged from a compressor and a super-heating degree at a refrigerant outlet side of an evaporator.
It is an another object of the present invention to provide a refrigerant cycle system with a compact structure, which can improve a cycle efficiency.
According to the present invention, in a refrigerant cycle system, a condenser for cooling and condensing refrigerant discharged from a compressor includes a first heat exchange unit, a second heat exchange unit at a downstream side of the first heat exchange unit in a refrigerant flow direction, and a gas liquid separator arranged between the first heat exchange unit and the second heat exchange unit in the refrigerant flow direction in such a manner that refrigerant discharged from a compressor is cooled in the first heat exchange unit and at least gas refrigerant separated in the gas-liquid separator flows into the second heat exchange unit. In the condenser, a refrigerant state flowing from the first heat exchange unit to the gas-liquid separator is changed in accordance with a super-heating degree of refrigerant discharged from the compressor to change a liquid refrigerant amount stored in the gas-liquid separator. The refrigerant state discharged from the compressor is in a super-heating state determined by a heat-exchanging amount of the first heat exchange unit, and a compression process of refrigerant in the compressor is basically an isoentropic change due to adiabatic compression. Accordingly, when the super-heating degree of refrigerant discharged from the compressor changes, the refrigerant state from the first heat exchange unit to the gas-liquid separator is changed, and the amount of liquid refrigerant stored in the gas-liquid separator is changed. Thus, the super-heating degree of refrigerant discharged from the compressor can be controlled in a predetermined area, and the super-heating degree of refrigerant at an outlet of an evaporator can be controlled in a predetermined area.
Preferably, a communication path through which liquid refrigerant stored in the gas-liquid separator is introduced into an upstream side of the decompression device in the refrigerant flow direction. Accordingly, it can prevent a refrigerant shortage in the refrigerant cycle system, and an oil shortage in the compressor.
On the other hand, the refrigerant cycle system has an adjustment member for adjusting an amount of liquid refrigerant stored in the gas-liquid separator in accordance with the super-heating degree of refrigerant discharged from the compressor, and adjustment member reduces the amount of liquid refrigerant stored in the gas-liquid separator when the super-heating degree of refrigerant discharged from the compressor increases. Accordingly, when the super-heating degree of refrigerant discharged from the compressor increases, the amount of liquid refrigerant in the gas-liquid separator is reduced by the adjustment member, and the flow amount of refrigerant circulating in the refrigerant cycle system is increased. Therefore, it can restrict an increase of the super-heating degree of refrigerant at the outlet of the evaporator and an increase of the super-heating degree of refrigerant discharged from the compressor. Conversely, when the super-heating degree of refrigerant discharged from the compressor decreases, the amount of liquid refrigerant in the gas-liquid separator is increased by the adjustment member, and the flow amount of refrigerant circulating in the refrigerant cycle system is decreased. Therefore, it can restrict a decrease of the super-heating degree of refrigerant at the outlet of the evaporator and a decrease of the super-heating degree of refrigerant discharged from the compressor.
Preferably, the first heat exchange unit and the second heat exchange unit are disposed integrally to have a plurality of tubes disposed in parallel with each other, through which refrigerant flows. Accordingly, attachment structure of the first heat exchange unit and the second heat exchange unit can be made simple. More preferably, the gas-liquid separator is disposed to be integrated with any one of the first and second header tanks.
Preferably, the adjustment member is a heating unit for adjusting a heating amount of liquid refrigerant in the gas-liquid separator in accordance with the super-heating degree of refrigerant discharged from the compressor. Therefore, the amount of liquid refrigerant stored in the gas-liquid separator can be readily controlled.
In the refrigerant cycle system, refrigerant flows through the compressor, a condenser, a decompression device and the evaporator in this order through a main refrigerant passage. The adjustment member includes a communication path through which liquid refrigerant in the gas-liquid separator returns to the main refrigerant passage, and a valve disposed in the communication path to increase a valve opening degree in accordance with an increase of the super-heating degree of refrigerant discharged from the compressor. Accordingly, the super-heating degree of refrigerant discharged from the compressor can be readily controlled using the adjustment member.
The gas-liquid separator can be disposed to return both gas refrigerant and liquid refrigerant separated from each other in the gas-liquid separator to the main refrigerant passage within the condenser. Therefore, the structure of the condenser including the gas-liquid separator can be made compact. Even in this case, because the amount of liquid refrigerant stored in the gas-liquid separator can be adjusted in accordance with the super-heating degree of refrigerant discharged from the compressor, the cycle efficient can be improved.
The condenser includes an inlet flow path provided between the first header tank and the gas-liquid separator, through which a part of refrigerant in a refrigerant passage of the condenser is introduced into the gas-liquid separator, a gas return passage through which gas refrigerant within the gas-liquid separator is introduced into the refrigerant passage at a downstream side position from the inlet flow path in the refrigerant flow direction, and a liquid return passage through which liquid refrigerant within the gas-liquid separator is introduced into the refrigerant passage at a downstream side position from the inlet flow path in the refrigerant flow direction. Accordingly, a volume of the gas-liquid separator of the condenser can be made smaller, while the super-heating degree of refrigerant discharged from the compressor can be readily controlled.